1. Field of the Invention
The present invention generally relates to load regulation, and more particularly to load regulation by using pulse width modulation (PWM).
2. Description of the Prior Art
The detection of current plays an important role in electronic circuits, especially in power supply circuits. The power supply circuit provides the electronic circuit with needed current in a manner similar to that the human heart continuously provides the body with blood. As high blood pressure is harmful to health and thus precisely measuring the blood pressure is necessary, likewise precisely and instantaneously detecting the current is vital to the controllability of the electronic circuits. The current is conventionally detected by measuring the voltage drop across a resistor of known low resistance according to Ohm's law. However, this scheme has some disadvantages. Firstly, the accuracy of the current detection would be probably affected by the inaccuracy of the resistor itself, and by the environmental factors, such as temperature variation. Secondly, the resistor wastefully consumes power and generates heat, especially when the current becomes large.
The detection of the load current in a computer motherboard is conventionally accomplished by using a temperature sensor such as a thermistor, whose resistance varies according to the surface temperature of the load under detect, such as a central processing unit (CPU). The thermistor is then utilized to control a fan for dissipating the heat generated from the load. Unfortunately, the thermistor usually responds slowly, and therefore a real-time monitoring and controlling the system becomes difficult. FIG. 1 shows the relationship between the rotational (or spin) speed of the fan and the detected CPU temperature. The fan rotates faster when high temperature is detected, and conversely, the fan rotates slower when low temperature is detected. Another conventional way of detecting the load current is performed by an indirect and software manner. Specifically, a Windows application program interface (API) is used to read the utility rate of the CPU. A high utility rate indicates high load current, and conversely, a low utility rate indicates low load current. The detection by using such API possesses drawbacks existing in general software programs in that the operations sometimes cause delay, hang, or even crash, not to say such API is not supported by every system.
For overcoming the disadvantages mentioned above, a need has arisen to propose a system and method for effectively and spontaneously monitoring and adjusting the load of an electronic circuit.